Alumina particles, production process thereof, composition comprising the particles and alumina slurry for polishing

ABSTRACT

Alumina particles obtained from aluminum chloride by a gas phase method, the alumina having an amorphous form or a crystalline form of transition alumina, with primary particles thereof having an average particle diameter of approximately 5 to 100 nm, and secondary particles, resulting from the aggregation of the primary particles, having an average particle diameter of approximately 150 to 800 nm and wherein the particles having a secondary particle diameter larger than 45 μm are contained in an amount of about 0.05% by mass or less.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/179,268, filed Jun. 26, 2002, which is a continuation-in-part (CIP)application under 35 U.S.C. §120 of U.S. patent application Ser. No.09/891,456 filed on Jun. 27, 2001 and PCT/JP00/09231 filed on Dec. 26,2000 and designating U.S., claiming benefit pursuant to 35 U.S.C.§119(e)(1) of the filing date of the Provisional Application 60/214,795filed on Jun. 28, 2000 pursuant to 35 U.S.C. §111(b).

TECHNICAL FIELD

The present invention relates to alumina particles obtained using a gasphase method, a process for producing the alumina particles, and acomposition comprising the particles. The alumina particles areobtainable from aluminum chloride by the gas phase method, and aresuitable for use as a slurry for polishing.

BACKGROUND ART

Aluminum oxide (alumina) has various crystalline forms such as γ-, δ-,θ-, and α-forms. The α-alumina is widely used as a raw material for fineceramics in most general use. The γ-, δ-, and θ-aluminas other than theα-alumina are low-temperature phases of the α-alumina. They are referredto as transition alumina and used for catalyst carriers, various kindsof fillers, and modifiers for modifying rheological properties.

To produce the transition alumina, there is a process of calciningaluminum hydroxide, aluminum alkoxide, or alum, followed by grinding.Calcination of aluminum hydroxide, aluminum alkoxide, and alum canremove water, alcohol, and ammonium sulfate respectively therefrom,thereby providing alumina. In the above process, the particle propertiesof the raw material and the calcining conditions strongly influence theprimary particle diameter and the secondary particle diameter of aluminaobtained as the resulting product. Therefore, in order to control theprimary and secondary particle diameters, it is important to payattention to the properties of the raw particles, specifically, toappropriately select the raw materials. The step of grinding thecalcined powder often becomes indispensable for regulating the particlesize.

Further, as examples of the process for obtaining the transition aluminaby synthesizing a raw material in a liquid phase and calcining the rawmaterial, the following processes are known: a process for obtainingγ-alumina by preparing basic aluminum ammonium carbonate in a liquidphase and calcining the basic aluminum ammonium carbonate (JapaneseLaid-Open Patent Application No. 11-228132); a process of gelling abasic aluminum chloride aqueous solution by pH adjustment and sinteringthe resulting gelled product (Japanese Laid-Open Patent Application No.11-228131); and a process of sintering and grinding hydrated aluminawith a boehmite structure (Japanese Laid-Open Patent Application No.11-268911).

In addition to the above, there is a process for obtaining thetransition alumina by a gas phase method, for example, a process forobtaining an ultrafine oxide by melting and vaporizing a metal in avacuum vessel, and introducing the vaporized metal into an oxidizingatmosphere; a process of evaporating and oxidizing a metal aluminumpowder in an oxygen-containing flame (Japanese Patent Publication No.5-53722); and a process of ejecting a metal halide represented byanhydrous aluminum chloride into a burner flame to oxidize the same(Japanese Laid-Open Patent Application No. 8-197414). The transitionalumina particles produced by such gas phase methods have a loweraggregation degree as compared with those of transition alumina producedthrough a liquid phase, or have a nearly spherical shape and are inalmost a monodispersed state.

Recently, there has been a tendency for more and more increase in thedegree of integration of circuits provided on a semiconductor substrate.The technique of chemical mechanical polishing (CMP) is attractingspecial attention as a method for increasing the degree of integration.In this technique, circuit formation on a substrate and smoothing of thesubstrate by polishing are alternately carried out to make amulti-layered circuit, thereby increasing the degree of integration. Aslurry used for the CMP comprises an aqueous solvent of which the liquidproperties are adjusted with an oxidizing metallic salt, a surfactant orthe like, and inorganic particles uniformly suspended in the solvent.The aqueous solvent chemically reacts with the surface subjected topolishing, and the compounds present on the surface subjected topolishing are scraped away by the mechanical abrasiveness of theinorganic particles. Therefore, the inorganic particles are required toefficiently work to scrape away the compounds with a measure of hardnessand to include neither coarse particles nor particles with extremelyhigh hardness, as both types of particles would cause scratches on thesurface subjected to polishing.

The transition alumina prepared through the sintering step includes alarge number of coarse particles. It is difficult to decrease the numberof coarse particles in order to cope with the CMP even if grinding isinsistently conducted. Further, variance in sintering in the particlesis unavoidable, and it is therefore highly probable that particles withhigh hardness are mixed in. Meanwhile, when the particles produced bythe gas phase method are spherical or nearly spherical, the frictionalforce of the particles against the surface subjected to polishingbecomes low and, consequently, the abrasiveness is decreased. In orderto improve the abrasiveness, it is better for the primary particles orsecondary particles to be large. However, scattering in the particlesize distribution is unavoidable in light of the properties of theparticles, so that no particles with a completely uniform particle sizeexist. On this account, with the increase in size of the primaryparticles or the secondary particles, the probability that coarseparticles are contained is drastically increased, with the result thatthe occurrence of scratches becomes frequent. The above-mentionedJapanese Laid-Open Patent Application No. 8-197414 discloses fumedalumina produced by a gas phase method. However, the previouslymentioned points are not taken into consideration, and the productionprocess is not disclosed.

SUMMARY OF THE INVENTION

The object of the present invention is to provide alumina particles withexcellent abrasiveness, containing small amounts of coarse particles tosuch a degree that the alumina particles are suitable as abrasive grainsfor CMP, a process for producing the alumina particles, and acomposition and an alumina slurry for polishing, each comprising thealumina particles.

The present inventors have intensively studied and succeeded inobtaining alumina particles capable of solving the above-mentionedproblems by controlling the manufacturing conditions such as mixing ofgases and the reaction temperature in the production process of aluminawhere aluminum chloride serving as a raw material is vaporized andthereafter allowed to react with an oxidizing gas.

Namely, the present invention basically provides the following:

(1) Alumina particles obtained from aluminum chloride by a gas phasemethod, the alumina having an amorphous form or being an alumina havinga crystalline form of transition alumina, with primary particles thereofhaving an average particle diameter of approximately 5 to 100 nm, andsecondary particles, resulting from the aggregation of the primaryparticles, having an average particle diameter of approximately 50 to800 nm.

(2) Alumina particles obtained from aluminum chloride by a gas phasemethod, the particles having an amorphous form or a γ-, δ-, or θ-crystalline form or a mixed form thereof, with primary particles thereofhaving an average particle diameter of approximately 5 to 100 nm, andsecondary particles, resulting from the aggregation of the primaryparticles, having an average particle diameter of approximately 50 to800 nm.

(3) The alumina particles as described in (1) or (2) above, whereinparticles having a particle diameter larger than 45 μm are contained inan amount of about 0.05% by mass or less.

(4) A process for producing alumina particles, comprising vaporizingaluminum chloride and high-temperature oxidizing the vaporized aluminumchloride with an oxidizing gas to produce alumina particles as describedin any one of (1) to (3) above.

(5) The process for producing alumina particles as described in (4)above, wherein the aluminum chloride vaporized gas and the oxidizing gasare preheated to 500° C. or more before the high-temperature oxidation.

(6) The process for producing alumina particles as described in any oneof (1) to (4) above, wherein the aluminum chloride-containing gas(material gas) and the oxidizing gas are introduced into a reactor eachat an ejecting flow velocity of about 10 m/sec or more, the ratio of theflow velocity of oxidizing gas to the flow velocity of material gas isapproximately from 0.2 to less than 10, and the amount of oxidizing gasis about 1 or more times the amount of oxidizing gas necessary forstoichiometrically oxidizing aluminum chloride.

(7) The process for producing alumina particles as described in any oneof (4) to (6) above, wherein the vaporized aluminum chloride gascontains approximately from 5 to 90% by volume of aluminum chloride.

(8) The process for producing alumina particles as described in any oneof (4) to (7) above, wherein the ratio of oxygen to water vapor in theoxidizing gas is from 0 to about 90% by volume of oxygen to from about10 to 100% by volume of water vapor and the sum total of oxygen andwater vapor is from about 10 to 100% by volume.

(9) The process for producing alumina particles as described in any oneof (4) to (8) above, wherein the high-temperature oxidation is performedwith a reactor residence time of about 1 sec or less.

(10) Alumina particles obtained by the production process of aluminaparticles described in any one of (4) to (9) above.

(11) A composition comprising alumina particles described in any one of(1) to (3) and (10) above.

(12) An alumina slurry for polishing, comprising alumina particlesdescribed in any one of (1) to (3) and (10) above.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram showing one example of a system flow which issuitably used for the production of alumina particles of the presentinvention.

BEST MODES FOR CARRYING OUT THE INVENTION

One embodiment of the present invention is described in detail below byreferring to the attached drawing, however, the present invention is notlimited to this embodiment.

FIG. 1 shows one example of a system flow which is suitably used for theproduction of alumina particles of the present invention. The systemstructure comprises a raw material feeder 1, a raw material sublimationvessel 2, an inert gas preheater 3, a material gas heater 4, anoxidizing gas heater 5, a reactor 6, a cooler 7 and a product collector8.

The production of alumina particles of the present invention is brieflydescribed below. Aluminum chloride A is fed to the raw materialsublimation vessel 2 by the raw material feeder 1. Simultaneously, theinert gas B is preheated by the inert gas preheater 3 and then fed tothe raw material sublimation vessel 2. The material gas C generated fromthe raw material sublimation vessel 2 is subsequently introduced intothe material gas heater 4. The raw material sublimation vessel 2 and thematerial gas heater 4 may be integrated into one body. The thus-heatedmaterial gas C containing aluminum chloride gas is introduced into thereactor 5. On the other hand, the oxidizing gas D is heated by theoxidizing gas heater 6 and then introduced into the reactor 5. After thealuminum chloride is completely oxidized in the reactor 5, a largequantity of cooling gas E is introduced into the cooler 7 to forciblyterminate the reaction. The reaction product is collected using acollector 8 such as bag filter, thereby obtaining a product P. Theexhaust gas is fed to an exhaust gas treating apparatus (not shown).

The alumina particles of the present invention are obtained byvaporizing the raw material aluminum chloride and oxidizing thevaporized aluminum chloride using an oxidizing gas by a gas phasemethod. The resultant alumina is an amorphous alumina or a transitionalumina which can have any of the crystalline forms, for example,γ-form, δ-form, and θ-form.

These particles are composed of particles with different particlediameters. The average primary particle diameter is approximately from 5to 100 nm, and the primary particles are loosely aggregated to form thesecondary particles with an average particle diameter herein used is aparticle diameter converted from a specific surface area measured by aBET method, namely, an average particle diameter calculated using aspecific surface area measured by a BET single point method (accordingto JIS R1626), and the average secondary particle diameter is an averageparticle diameter determined by a laser Doppler type particle sizemeasuring apparatus. The procedure of measuring the particle sizedistribution is described below. 50 ml of pure water and 100 μl of anaqueous 10% sodium hexametaphosphate solution are added to 0.05 g ofalumina particles and on the obtained slurry, ultrasonic waves (46 KHz,65 W) are irradiated for 3 minutes. The resulting slurry is subjected tothe measurement of particle size distribution in a laserdiffraction-type particle size distribution measuring device(“SALD-2000J”, manufactured by Shimadzu Corporation). From thethus-measured particle size distribution, the average secondary particlesize may be calculated. When the average primary particle diameter isless than about 5 nm and/or the average secondary particle diameter isless than about 50 nm, the abrasiveness is insufficient. When theaverage primary particle diameter exceeds about 100 nm and the averagesecondary particle diameter exceeds about 800 nm, the occurrence ofscratches becomes frequent in the course of polishing.

The reason why the alumina particles of the present invention aresuitable for CMP has not been clarified. However, it is presumed thatthe polishing rate can be very effectively accelerated due to the factthat the primary particle diameters or the secondary particle diametersare appropriately large and the particles have a complicated shaperesulting from the aggregation. With regard to the particles that causethe scratches, it is considered that when the alumina particles of thepresent invention have average particle diameters within theabove-mentioned ranges, coarse particles, if included, are easilydisintegrated by the pressure applied thereto in the polishing operationbecause the primary particles are loosely aggregated to constitute thesecondary particles. Although the coarse particles can be disintegrated,it is preferable to reduce the amount of such coarse particles. Forexample, 50 g of the powder is added to 0.3 liter of pure water, and theresultant mixture is stirred and dispersed by the application ofultrasonic waves thereto for 2 minutes to prepare a slurry, followed byclassifying with a sieve. In this case, it is preferable that particleshaving a diameter of 45 μm or more (above 45 μm mesh) be contained in anamount of about 0.05 mass % or less. It is considered that the looseaggregation of the primary particles is inherent in the particlesproduced by the gas phase method according to the present invention.Further, the alumina of the present invention is amorphous, or γ, δ, orθ-form, and it is considered that the hardness of the particle itself islower than that of α-alumina particle, so that scratches are scarcelyproduced.

As described above, the alumina particles of the present invention areobtained by subjecting an aluminum chloride gas to high temperatureoxidation using an oxidizing gas. The aluminum chloride (usually,aluminum chloride anhydrous) serving as a raw material for the aluminumchloride gas is in a powdered state at room temperatures, and isintroduced into a raw material sublimation vessel 2 and gasified.

At this time, the aluminum chloride gas may be diluted with a dilutinggas. The diluting gas must be selected from those incapable of reactingwith aluminum chloride and free of oxidation. An inert gas B ispreferably used as a carrier gas. This inert gas B also functions as asealing gas at the time of introducing raw materials. Examples of theinert gas B include nitrogen, helium and argon, but the inert gas is notlimited thereto. For efficient gasification of aluminum chloride A, theinert gas B may be preheated before introducing it to the raw materialsublimation vessel 2. The temperature at the preheating of inert gas Bis about 30° C. or more, preferably about 50° C. or more, morepreferably about 200° C. or more. The preheating temperature differenceis preferably as small as possible, however, the preheating temperaturemay be selected from the range of not exceeding about 300° C. accordingto the objective particle size.

The inert gas is introduced into the raw material sublimation vessel 2so that the ratio of AlCl₃/(AlCl₃+inert gas) is approximately from 5 to90% by volume, preferably from about 5 to about 80% by volume, morepreferably from about 7 to about 80% by volume. This concentration isclosely related to the productivity and therefore, is a factor forcontrolling the particle diameter of alumina primary particles. Morespecifically, with an aluminum chloride (AlCl₃) concentration ofapproximately 5 to 90% by volume, a large number of uniform nuclei aregenerated or the reactivity increases, as a result, the formation ofparticles grown under the CVD governance is hindered and the obtainedparticles can have a narrow particle size distribution.

Subsequently, the aluminum chloride gas, optionally comprising the inertgas, in other words, the material gas C, is introduced into a materialgas heater 4 connected to the raw material sublimation vessel 2 andheated. For heating, a glass or ceramic heater is used. Further, byfilling the material gas heater 4 with a heat transfer medium, the heattransfer to the material gas C can be more efficiently promoted. As theheat transfer medium, heat-resistant materials such as ceramics andglass, in particular, quartz glass and alumina ceramics are preferable.In view of the heat transfer efficiency, it is preferable that themedium be in the shape of a circular ring, mesh ring, honeycomb, orRasching ring. The amount of heat transfer medium with which the heateris filled is determined in consideration of thermal expansion andpressure loss. The diameter and the length of the heater are determinedso that the temperature of the material gas at the ejecting port of thematerial gas heater 4 is preferably about 500° C. or more, and morepreferably about 600° C. or more. The upper limit of the material gastemperature is about 1,300° C. If this preheating temperature is lessthan about 500° C., uniform nuclei are scarcely generated and thereactivity is low, as a result, the obtained aluminum particles have abroad particle size distribution. The preheating temperature may besufficient if it is lower than the reaction temperature described below.

It is preferable that a heater 6 for the oxidizing gas has the samestructure as the material gas heater 4. The oxidizing gas means oxygen,water vapor, or a mixed gas comprising oxygen and water vapor. Thetemperature at the ejecting port is preferably about 500° C. or more,and more preferably about 600° C. or more. The upper limit of thetemperature is the same as that of the material gas. If this peheatingtemperature is less than about 500° C., uniform nuclei are scarcelygenerated and the reactivity is low and, as a result, the obtainedaluminum particles have a broad particle size distribution. Thepreheating temperature may be sufficient if it is lower than thereaction temperature described below.

An oxidizing gas B having a composition of 0 to about 90% by volume ofoxygen and about 10 to 100% by volume of water vapor, with the totalamount of oxygen and water vapor being in the range of about 10 to 100%by volume, is usually employed. In the case where the sum of oxygen andwater vapor does not reach 100%, the residual gas is a non-oxidizing gassuch as nitrogen. Water vapor is used because water vapor has been foundto very effectively accelerate the oxidation of the aluminum chloridegas.

The ratio of the amount of material gas C to oxidizing gas D isdetermined so that the flow velocity ratio of gases ejected from thenozzles, that is, the ratio of the flow velocity of the oxidizing gas tothe flow velocity of the material gas, may range approximately from 0.2to less, than 10, preferably from about 0.2 to less than about 5, morepreferably from about 0.3 to less than about 2. If this flow velocityratio between gases is less than about 0.2, the gas flow in the reactor5 has a conspicuous partiality and aluminum chloride is generated anddeposited on the wall surface of the reactor 5 or in the collector 8,causing choking of the reactor 5 or collector 8 or contamination of theresulting product. If the flow velocity ratio is about 10 or more, theflow velocity of material gas and the flow velocity of oxidizing gas arein bad balance and therefore, the oxidizing gas having a high flowvelocity enters the nozzle side of ejecting the material gas having alow flow velocity and reacts in the vicinity of the nozzle to generatescaling and thereby cause choking of the nozzle.

At the same time, the ratio of the amount between the gases isdetermined so that the ejecting flow velocity of each gas is about 10m/sec or more, preferably about 20 to about 200 m/sec, more preferablyabout 30 to about 150 m/sec, and that the oxidizing gas is in an amountof 1 or more times, preferably about 1 to about 10 times, morepreferably about 1 to about 4 times, the amount that isstoichiometrically required to oxidize the aluminum chloride. The gasflow velocity is calculated from the flow rate, the temperature, and theejection area of the nozzle.

The material gas C and the oxidizing gas D are introduced into a reactor5. As long as each of the gas compositions is as previously defined andthe amount ratio of the gases is within the above-mentioned range, theoxidation smoothly proceeds using any of the gas introducing systemssuch as parallel flow system, counter flow system, crossed flow system,and oblique flow system. In particular, it is preferable that theejecting port for introduction employs a coaxial parallel flow systemusing a coaxial double nozzle with an internal tube for the materialgas, and an external tube for the oxidizing gas.

In any case, to prevent the resultant product from being contaminatedwith aluminum chloride, the amount of oxidizing gas D must be set to thesame or greater than the stoichiometric amount required to oxidizealuminum chloride.

The size of the reactor 5 is determined so that the reactor residencetime is preferably about 1 second or less, more preferably about 0.1second or less, still more preferably about 0.07 second or less. Thereactor residence time is obtained by calculating the amount of gasgenerated after the oxidation reaction from the flow rate of gasintroduced into the reactor 5, at standard state, and dividing thecalculated amount of gas by the volume of the reactor 5. The residencetime is closely related to the characteristics of alumina particles,namely, the secondary particle diameter, and therefore, the particlesize can be appropriately changed by varying the residence time.However, the residence time over 1 second is not preferable because thesecondary particle diameter becomes too large, thereby increasing thenumber of coarse particles.

The reactor 5 for use in the present invention may have any shape. Acylindrical form is advantageous in view of the prevention of scalingand deposition. The material for the reactor is determined by takingaccount of the heat resistance at the time of performing the oxidationreaction of the aluminum chloride gas and the corrosion resistanceagainst the oxidizing gas atmosphere. Preferable examples of thematerial are metallic titanium, graphite (water-cooled), and quartzglass. The oxidation reaction of the aluminum chloride gas proceeds inthe high-temperature reactor 5.

In the present invention, the flow velocity of gas introduced into thereaction tube is preferably high so as to completely mix the gases inthe reaction tube and, more preferably about 5 m/sec or more in terms ofthe average flow velocity. With a gas flow velocity of about 5 m/sec ormore in the reaction tube, thorough mixing can be attained in thereaction tube, as a result, the formation of particles grown under theCVD governance is reduced and the produced particles can be preventedfrom having a broad particle size distribution.

After the oxidation reaction, rapid cooling becomes necessary to controlthe particle size of the secondary particles. To be more specific, amethod of introducing a gas obtained after the reaction into a cooler 7connected to the reactor 5 is adopted, with a cooling gas E beingsupplied to the cooler 7. Air or nitrogen is used as the cooling gas E,and such a cooling gas is blown into the cooler 7 so that the averagegas temperature in the cooler 7 is approximately from 100 to 450° C.,preferably from about 100 to about 400° C., more preferably from about100 to about 350° C. The lower the average gas temperature the better.However, this necessitates large quantities of cooling gas, so that theabove-mentioned gas temperature range is suitable when the prevention ofmoisture condensation in the gas is also taken into consideration. Thealumina particles are inhibited from growing in this way, and arecollected using a collector 8 such as bag filter. Simultaneously,exhaust gas is discharged from the collector 8 and sent to an exhaustgas treating apparatus (not shown). The primary particle diameter andthe secondary particle diameter of the alumina particles can becontrolled by changing the temperatures of the material gas C and theoxidizing gas D, the concentration of the material gas, the reactorresidence time, and the flow velocities of the gases, ejected into thereactor 5.

The alumina particles collected by the collector 8 such as a bag filtermay be heated to reduce the content of chlorine (Cl). For this purpose,an electric furnace or externally heated rotary kiln may be used. Inthis case, the heating temperature is approximately from 150 to 850° C.,preferably from about 150 to about 550° C., more preferably from about200 to about 500° C. If the heating temperature is less than about 150°C., chlorine cannot be satisfactorily removed, whereas if it exceedsabout 850° C., the quality of alumina product disadvantageouslydecreases.

By employing the manufacturing conditions and the system structure asdescribed above, it is possible to continuously provide aluminaparticles having a primary particle diameter approximately of 5 to 100nm and a secondary particle diameter of approximately 50 to 800 nm, withan amorphous, γ-, δ-, or θ-crystalline form.

The alumina particles can be prepared as a slurry suitable for polishingthe semiconductor substrate or the like by dispersing the aluminaparticles in water, with the addition thereto of a pH adjustor and apolishing accelerator in accordance with the conventional process.Further, a composition is prepared by mixing the alumina particles, anorganic solvent (for example, an alcohol or a ketone), and the like. Thecomposition may be used as a coating agent for paper or the like.

EXAMPLES

The present invention will be explained with reference to the followingexamples and comparative example, but the present invention is notintended to be limited by the examples.

Evaluation of Polishing

1) Polishing Method

A polishing slurry was prepared by dissolving 3.5 mass % of iron nitraterionahydrate (a guaranteed reagent produced by Kanto Chemical Co., Inc.)in water to prepare an aqueous solution, and uniformly dispersing 2 mass% of alumina particles in the aqueous solution. The abrasiveness isevaluated in terms of the polishing rate, the selecting ratio, and thepresence of scratches. The selecting ratio is a ratio of the polishingrate of a metal subjected to polishing, such as tungsten, to thepolishing rate of an insulating film for which polishing is notdesirable. As this ratio is larger, the performance of the polishingslurry is higher because the metal is polished and the insulating filmis not polished.

2) Evaluation of Polishing Rate

The polishing rate was evaluated by the following procedure. Fivetungsten plates each having a diameter of 20 mm and a thickness of 5 mm(purity of 99.9 mass %) were attached to a glass substrate having adiameter of 110 mm and a thickness of 5 mm to prepare a work material tobe subjected to polishing. The polishing pad used was a semiconductordevice-polishing two-layered pad (“IC1000/Suba400” manufactured by RODELNITTA Company). The polishing machine used was a single-side polishingmachine with a surface table having a diameter of 320 mm, “Model7941-338” manufactured by Marumoto Kogyo K.K. The polishing wasperformed at 60 rpm by the application of a 39.2 kPa pressure whilefeeding the polishing slurry at a rate of 10 ml/min. After the polishingwas performed under such conditions for 15 minutes, the polishing ratewas calculated in terms of the thickness from the weight change of thework material.

3) Evaluation of Selecting Ratio

A thermally oxidized film formed on a silicon substrate was subjected topolishing and the polishing rate was obtained. From the polishing rateof the silicon substrate and the polishing rate of the above-describedtungsten plate, the selecting ratio was calculated. The thermallyoxidized film formed on a silicon wafer with a diameter of 6 inches anda thickness of 625 μm was subjected to polishing, using a semiconductordevice-polishing two-layered pad (“IC1000/Suba400” manufactured by RODELNITTA Company) as the polishing pad. The polishing machine used was asemiconductor device-polishing single-side polishing machine having asurface table with a diameter of 320 mm, “Model SH-24” manufactured bySpeedFam Co., Ltd. The polishing was performed at 30 rpm by theapplication of a 39.2 kPa pressure while feeding the polishing slurry ata rate of 10 ml/min. After the polishing was performed under suchconditions for 1 minute, the polishing rate was calculated using a lightinterference film thickness gauge.

4) Evaluation of Scratches

The evaluation of scratches was performed on five levels by counting thenumber of scratches in 10 visual fields through observation under adifferential interference microscope (at a magnification of 50 times).The evaluation criteria are as follows.

1: The number of scratches was 0 to 1.

2: The number of scratches was 2 to 10.

3: The number of scratches was 10 to 50.

4: The number of scratches was 50 to 100.

5: The number of scratches was 100 or more.

Example 1

Using 9.4 Nm³/hr (“N” means standard state) of a nitrogen gas heated at500° C. as a carrier gas, anhydrous aluminum chloride was fed to a rawmaterial sublimation vessel at a flow rate of 51 kg/hr. A gas comprisingthe aluminum chloride gas generated from the sublimation vessel wasintroduced into a heater. This heater was an externally heated typeheater and filled with siliceous stone. The temperature of the materialgas obtained in the heater was 850° C. when measured at an ejecting portto a reactor. The concentration of raw material was 48% by volume andthe ejecting flow velocity was 83 m/sec.

Separately, 68 Nm³/hr in total of an oxidizing gas comprising 95% byvolume of water vapor and 5% by volume of oxygen was heated by anexternally heated type heater. The heater was filled with siliceousstone. The temperature of the heated oxidizing gas was 850° C. whenmeasured at an ejecting port to the reactor. The ejecting flow velocitywas 34 m/sec. These two gases were ejected into the reactor by a coaxialdouble tube parallel flow system, and the ratio of the flow velocity ofthe oxidizing gas to the flow velocity of the material gas was 0.41. Theaverage residence time was 0.3 seconds in the reactor. Immediately afterthe gas passed the outlet of the reactor, the gas temperature waslowered to 300° C. or less by blowing air at room temperature. Thealumina particles collected thereafter by a bag filter were γ-aluminahaving an average primary particle diameter of 45 nm and an averagesecondary particle diameter of 300 nm. When this alumina wasfractionated by wet sieving with a mesh size of 45 μm, the remainingparticles above sieve amounted to 0.005 mass %. The polishing propertiesof the obtained alumina particles were evaluated. The polishing rate oftungsten was 7,100 Å/min, the selecting ratio was 510, and the presenceof scratches was evaluated as level 2.

Example 2

Using 11.4 Nm³/hr of a nitrogen gas heated at 500° C. as a carrier gas,aluminum chloride anhydrous was fed to a raw material sublimation vesselat a flow rate of 47 kg/hr. A gas comprising the aluminum chloride gasgenerated from the sublimation vessel was introduced into a heater. Thisheater was an externally heated type heater and filled with siliceousstone. The temperature of the material gas obtained in the heater was830° C. when measured at an ejecting port to a reactor. Theconcentration of raw material was 41% by volume and the ejecting flowvelocity was 72 m/sec.

Separately, 118 Nm³/hr of an oxidizing gas comprising 100% by volume ofwater vapor was heated by an externally heated type heater. The heaterwas filled with siliceous stone. The temperature of the heated oxidizinggas was 835° C. when measured at an ejecting port to the reactor. Theejecting flow velocity was 179 m/sec. These two gases were ejected intothe reactor by a coaxial double tube parallel flow system, and the ratioof the flow velocity of the oxidizing gas to the flow velocity of thematerial gas was 2.5. The average residence time was 0.04 seconds in thereactor. Immediately after the gas passed the outlet of the reactor, thegas temperature was lowered to 300° C. or less by blowing air at roomtemperature. The alumina particles collected thereafter by a bag filterwere γ-alumina having an average primary particle diameter of 30 nm andan average secondary particle diameter of 150 nm. When this alumina wasfractionated by wet sieving with a mesh size of 45 μm, the remainingparticles above mesh amounted to 0.002 mass %. The polishing propertiesof the obtained alumina particles were evaluated. The polishing rate oftungsten was 5,300 Å/min, the selecting ratio was 420, and the presenceof scratches was evaluated as in level 1.

Example 3

Using 11.4 Nm³/hr of a nitrogen gas heated at 500° C. as a carrier gas,anhydrous aluminum chloride was fed to a raw material sublimation vesselat a flow rate of 47 kg/hr. A gas comprising the aluminum chloride gasgenerated from the sublimation vessel was introduced into a heater. Thisheater was an externally heated type heater and filled with siliceousstone. The temperature of the material gas obtained in the heater was830° C. when measured at an ejecting port to a reactor. Theconcentration of raw material was 41% by volume and the ejecting flowvelocity was 72 m/sec.

Separately, 148 Nm³/hr in total of an oxidizing gas comprising 80% byvolume of water vapor and 20% by volume of oxygen was heated by anexternally heated type heater. The heater was filled with siliceousstone. The temperature of the heated oxidizing gas was 830° C. whenmeasured at an ejecting port to the reactor. The ejecting flow velocitywas 200 m/sec. These two gases were ejected into the reactor by acoaxial double tube parallel flow system, and the ratio of the flowvelocity of the oxidizing gas to the flow velocity of the material gaswas 2.8. The average residence time was 0.03 seconds in the reactor.Immediately after the gas passed the outlet of the reactor, the gastemperature was lowered to 300° C. or less by blowing air at roomtemperature. The alumina particles collected thereafter by a bag filterwere γ-alumina having an average primary particle diameter of 20 nm andan average secondary particle diameter of 80 nm. When this alumina wasfractionated by wet sieving with a mesh size of 45 μm, the remainingparticles above sieve amounted to 0.006 mass %. The polishing propertiesof the obtained alumina particles were evaluated. The polishing rate oftungsten was 5200 Å/min, the selecting ratio was 460, and the presenceof scratches was evaluated as level 2.

Example 4

Using 31 Nm³/hr of a nitrogen gas heated at 500° C. as a carrier gas,anhydrous aluminum chloride was fed to a raw material sublimation vesselat a flow rate of 43 kg/hr. A gas comprising the aluminum chloride gasgenerated from the sublimation vessel was introduced into a heater. Thisheater was an externally heated type heater and filled with siliceousstone. The temperature of the material gas obtained in the heater was800° C. when measured at an ejecting port to a reactor. Theconcentration of raw material was 19% by volume and the ejecting flowvelocity was 150 m/sec.

Separately, 118 Nm³/hr in total of an oxidizing gas comprising 60% byvolume of water vapor and 40% by volume of oxygen was heated by anexternally heated type heater. The heater was filled with siliceousstone. The temperature of the heated oxidizing gas was 800° C. whenmeasured at an ejecting port of the reactor. The ejecting flow velocitywas 90 m/sec. These two gases were ejected into the reactor by a coaxialdouble tube parallel flow system, and the ratio of the flow velocity ofthe oxidizing gas to the flow velocity of the material gas was 0.60. Theaverage residence time was 0.02 seconds in the reactor. Immediatelyafter the gas passed the outlet of the reactor, the gas temperature waslowered to 300° C. or less by blowing air at room temperature. Thealumina particles collected thereafter by a bag filter were amorphousalumina having an average primary particle diameter of 15 nm and anaverage secondary particle diameter of 70 nm. When this alumina wasfractionated by wet sieving with a mesh size of 45 μm, the remainingparticles above sieve amounted to 0.003 mass %. The polishing propertiesof the obtained alumina particles were evaluated. The polishing rate oftungsten was 4,000 Å/min, the selecting ratio was 560, and the presenceof scratches was evaluated as level 1.

Example 5

Using 30 Nm³/hr of a nitrogen gas heated at 500° C. as a carrier gas,anhydrous aluminum chloride was fed to a raw material sublimation vesselat a flow rate of 45 kg/hr. A gas comprising the aluminum chloride gasgenerated from the raw material sublimation vessel was introduced into amaterial gas heater. This material gas heater was an externally heatedtype heater and filled with a lump of an alumina sintered body. Thetemperature of the material gas obtained in the heater was 800° C. whenmeasured at an ejecting port to a reactor. The concentration of rawmaterial was 20% by volume and the ejecting flow velocity was 143 m/sec.

Separately, 450 Nm³/hr of an oxidizing gas comprising 100% by volume ofwater vapor was heated by an externally heated type oxidizing gasheater. The oxidizing gas heater was filled with a lump of an aluminasintered body. The temperature of the heated oxidizing gas was 880° C.when measured at an ejecting port of the reactor. The ejecting flowvelocity was 127 m/sec. These two gases were ejected into the reactor bya coaxial double tube parallel flow system, and the ratio of the flowvelocity of the oxidizing gas to the flow velocity of the material gaswas 1.1. The average residence time was 0.01 second in the reactor.Immediately after the gas passed the outlet of the reactor, the gastemperature was lowered to 300° C. or less by blowing air at roomtemperature. The alumina particles collected thereafter by a bag filterwere γ-alumina having an average primary particle diameter of 12 nm andan average secondary particle diameter of 300 nm. When this alumina wasfractionated by wet sieving with a mesh size of 45 μm, the remainingparticles above sieve amounted to 0.005 mass %. To 100 g of thisalumina, 900 g of an aqueous solution comprising 40 mass of polyvinylalcohol (124H, produced by Kuraray) was added and the resulting slurrywas milled in a homomixer (T.K ROBOMIX, manufactured by Tokushu KikaKogyo K.K.) at 11,000 rpm for 30 minutes to prepare a coating solution.This coating solution was coated on a resin coated paper by a bar coaterto a dry thickness of 20 μm and then dried. The coating film was free ofgeneration of cracks even after the drying. Using a color printer(BJC-465J, manufactured by Canon Inc.), the obtained recording paper wassubjected to a printing test, as a result, the ink absorptivity andcolor formation property both were very excellent. The same test wasperformed except for changing the substrate to polyethyleneterephthalate film (100 μm, produced by Toray Industries, Inc.), as aresult, the coating film further had good transparency.

Example 6

Using 11.4 Nm³/hr of a nitrogen gas heated at 500° C. as a carrier gas,aluminum chloride anhydrous was fed to a raw material sublimation vesselat a flow rate of 47 kg/hr. A gas comprising the aluminum chloride gasgenerated from the raw material sublimation vessel was introduced into amaterial gas heater. This material gas heater was an externally heatedtype heater and filled with a lump of alumina sintered body. Thetemperature of the material gas obtained in the heater was 830° C. whenmeasured at an ejecting port to a reactor. The concentration of rawmaterial was 41% by volume and the ejecting flow velocity was 72 m/sec.

Separately, 118 Nm³/hr of an oxidizing gas comprising 100% by volume ofwater vapor was heated by an externally heated type oxidizing gasheater. The oxidizing gas heater was filled with a lump of an aluminasintered body. The temperature of the heated oxidizing gas was 835° C.when measured at an ejecting port to the reactor. The ejecting flowvelocity was 179 m/sec. These two gases were ejected into the reactor bya coaxial double tube parallel flow system, and the ratio of the flowvelocity of the oxidizing gas to the flow velocity of the material gaswas 2.5. The average residence time was 0.04 seconds in the reactor.Immediately after the gas passed the outlet of the reactor, the gastemperature was lowered to 300° C. or less by blowing air at roomtemperature. The alumina particles collected thereafter by a bag filterwere γ-alumina having an average primary particle diameter of 30 nm andan average secondary particle diameter of 150 nm. When this alumina wasfractionated by wet sieving with a mesh size of 45 μm, the remainingparticles above sieve amounted to 0.002 mass %. The obtained aluminaparticles were mixed with a water-absorbing resin powder mainlycomprising sodium polyacrylate having an average particle diameter of500 μm. The mixing ratio was 0.3 mass % based on the mass ofwater-absorbing resin powder. The resulting mixed powder was leftstanding in a thermo-hygrostat at 35° C. and a relative humidity of 90%for 24 hours and thereafter, the state was examined. As a result, it wasfound that the resin was not fused.

Comparative Example 1

Alum was calcined in an electric furnace to obtain γ-alumina (80 m²/g).The obtained γ-alumina particles had an average primary particlediameter of 25 nm and an average secondary particle diameter of 5 μm.The alumina particles were subjected to wet milling using a ball milland alumina ball as the grinding medium, and then allowed to stand forclassification. The obtained alumina was γ-alumina having an averageprimary particle diameter of 25 nm and an average secondary particlediameter of 900 nm. When the γ-alumina was fractionated by wet sievingwith a mesh size of 45 μm, the remaining particles above sieve amountedto 0.6 mass %. The polishing properties of the obtained alumina wereevaluated. The polishing rate of tungsten was 4,200 Å/min, the selectingratio was 120, and the presence of scratches was evaluated as level 4.

Comparative Example 2

Aluminum hydroxide with a bayerite crystalline form having an averagesecondary particle diameter of 40 μm was sintered to obtain θ-alumina.The θ-alumina particles were subjected to wet milling using a ball milland an alumina ball as the grinding medium, and were then allowed tostand for classification. The obtained alumina was θ-alumina having anaverage primary particle diameter of 35 nm and an average secondaryparticle diameter of 1,500 nm. When this alumina was fractionated by wetsieving with a mesh size of 45 μm, the remaining particles above sieveamounted to 0.8 mass %. The polishing properties of the obtained aluminawere evaluated. The polishing rate of tungsten was 5,100 Å/min, theselecting ratio was 310, and the presence of scratches was evaluated aslevel 5.

The preparation conditions and the properties of the products obtainedin Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 1and the preparation conditions and the properties of the productsobtained in Examples 5 and 6 are shown in Table 2. TABLE 1 ComparativeComparative Example 1 Example 2 Example 3 Example 4 Example 1 Example 2Material Gas Alum was calcined Bayerite aluminum Flow velocity ofnitrogen 9.4 11.4 11.4 31 in an electric hydroxide with an gas (Nm³/hr)oven and wet average secondary Temperature (° C.) 500 500 500 500 milledby aluminum particle size of Flow velocity of raw 51 47 47 43 balls,followed 40 μm was fired material (kg/hr) by being placed to obtain θ-Concentration of raw 48 41 41 19 and classified. alumina, which material(% by volume) was wet milled Gas temperature (at the 850 830 830 800with alumina ejecting port) balls, followed Ejecting flow velocity 83 7272 150 by being placed (m/sec) and classified. Oxidizing Gas Compositionwater vapor 95 100 80 60 (% by volume) oxygen 5 0 20 40 (% by volume)Flow velocity (Nm³/hr) 68 118 148 118 Gas temperature (at the 850 835830 800 ejecting port) Ejecting flow velocity 34 179 200 90 (m/sec)Ratio of (flow velocity of 0.41 2.5 2.8 0.60 oxidizing gas)/(flowvelocity of material gas) Average residence time 0.3 0.04 0.03 0.02(sec) Alumina Crystalline form γ γ γ amorphous γ θ Average primaryparticle 45 30 20 15 25 35 diameter (nm) Average secondary particle 300150 80 70 700 1500 diameter (nm) Above sieve after 0.005 0.002 0.0060.003 0.6 0.8 fractionation by wet sieving with mesh size of 45 μm (mass%) Tungsten polishing rate 7100 5300 5200 4000 4200 5100 (Å/min)Selecting ratio 510 420 460 560 120 310 Evaluation of scratches 2 1 2 14 5

TABLE 2 Example 5 Example 5 Material Gas Flow velocity of nitrogen gas(Nm³/hr) 30 11.4 Temperature (° C.) 500 500 Flow velocity of rawmaterial (kg/hr) 45 47 Concentration of raw material 20 41 (% by volume)Gas temperature (at the ejecting port) 800 830 (° C.) Ejecting flowvelocity (m/sec) 143 72 Oxidizing Gas Composition water vapor (% byvolume) 100 100 oxygen (% by volume) 0 0 Flow velocity (Nm³/hr) 450 118Gas temperature (at the ejecting port) 880 835 (° C.) Ejecting flowvelocity (m/sec) 127 179 Ratio of (flow velocity of oxidizing 0.1 1.5gas)/(flow velocity of material gas) Average residence time (sec) 0.010.04 Alumina Crystalline form γ γ Average primary particle diameter (nm)12 30 Average secondary particle diameter (nm) 300 150 Above sieve afterfractionation by wet 0.005 0.002 sieving with mesh size of 45 μm (mass%) Generation of cracks in coating film None — (20 μm) after drying Inkabsorptivity good — Color formation of ink good — State after a mixturewith water- — No resin absorbing resin powder mainly fusion comprisingsodium fusion polyacrylate was found having an average particle size of500 μm (mixing ratio: 0.3 mass %) was left standing at 35° C. and arelative humidity of 90% for 24 hours

INDUSTRIAL APPLICABILITY

In the alumina particles of the present invention, the primary particlesare loosely aggregated to form the secondary particles. The alumina ofthe present invention is an amorphous alumina with a relatively lowhardness, or a transition alumina. Therefore, the alumina particles canbe used for not only the CMP application, but also the cosmeticsapplication where scrubbing and smooth feeling both are desired.Further, fine primary particles are aggregated properly, so that thealumina particles are also provided with adsorptivity of chemicalsubstances. On this account, when the alumina particles are used as acoating solution for a substrate such as paper or polymer film, anexcellent recording medium can be obtained, where the color of thesubstrate is not affected due to transparency and blurring of ink doesnot occur because of good ink absorptivity. Furthermore, the aluminaparticles of the present invention are favorably used as substitutes forconventional active alumina.

According to the present invention, the above-described aluminaparticles can be continuously produced with stable quality by industrialmass-production scale, so that the production process is considered tohave a great practical value.

The present invention can also be practiced according to other specificembodiments without departing from its essential feature. Accordingly,it is intended that the above-described embodiment is illustrative inall points and not restrictive, the scope of the present invention islimited not by this detailed description but rather by the claimsappended hereto, and all modifications within the scope and equivalenceof the appended claims are included within the scope of presentinvention.

1. Alumina particles obtained from aluminum chloride by a gas phasemethod, said alumina having an amorphous form or a crystalline form oftransition alumina, with primary particles thereof having an averageparticle diameter of approximately 5 to 100 nm, and secondary particles,resulting from the aggregation of said primary particles, having anaverage particle diameter of approximately 150 to 800 nm and wherein theparticles having a secondary particle diameter larger than 45 μm arecontained in an amount of about 0.05% by mass or less.
 2. Aluminaparticles obtained from aluminum chloride by a gas phase method, saidparticles having a crystalline form of δ or θ or a mixed form thereof.3. A composition comprising the alumina particles as set forth inclaim
 1. 4. A composition comprising the alumina particles as set forthin claim
 2. 5. An alumina slurry for polishing, comprising the aluminaparticles as set forth in claim
 1. 6. An alumina slurry for polishing,comprising the alumina particles as set forth in claim 2.